The prior art generally identifies residual oils reduced crude oils, atmospheric tower bottoms, topped crudes, vacuum resids, or simply heavy oils. These high boiling portions of crude oils are also known as comprising refractory components, such as polycyclic aromatics and asphaltenes, which are considered difficult to catalytically crack to form high yields of gasoline and tend to form higher boiling hydrocarbon fractions because of the deposition of large amounts of coke on the cracking catalyst. Furthermore, metal contaminants in these heavy oil fractions contain metals such as sodium, vanadium, nickel, copper and iron, which may be deposited on and/or in the pores of the catalyst thereby poisoning and/or inactivating the catalyst. The coking tendencies of the heavy oil fractions plus the heavy metals effect are so overpowering that zeolites subjected to such conditions are generally considered unacceptable for commercial processes.
Residual oils comprising relatively high boiling fractions of crude oil may be obtained as atmospheric tower bottoms and/or vacuum tower bottoms contained therein and are generally regarded as distress stocks by the petroleum industry because such oils contain large quantities of components generally considered to have strong coke forming tendencies, as well as having heavy metal components. For example, residual oils may contain carbon residues in excess of 0.6% by weight, and this characteristic is generally considered by the petroleum industry to contribute to the production of high coking in a cracking operation. This high coking in conjunction with the high heavy metal levels will operate to rapidly deactivate the cracking catalyst and, thus, lead to uneconomical operation of the cracking process. These problems have tended to result in expensive processes to effect the elimination of these materials from cracking feeds.
"Residual oils" for the purpose of this invention include crude oil fractions boiling between 400.degree. F. and the final end boiling point of a crude oil, often in excess of 1800.degree. F. The residual oil feedstock can be light gas oils boiling from about 400.degree. F. to 700.degree. F., medium gas oils boiling from about 600.degree. F. to 850.degree. F., heavy gas oils boiling from about 600.degree. F. to 1200.degree. F. and/or components boiling beyond 1200.degree. F. up to the final boiling point of the crude oil, including carbon producing components, such as polycyclic aromatics, asphaltenes and metal contaminants, as well as whole crudes. Separately prepared feedstocks, such as those prepared by solvent extraction of hydrogenated stocks, may also be employed as feedstocks in the process.
It is generally considered that the fluid catalytic cracking of hydrocarbon feeds containing components boiling beyond 1200.degree. F. leads to poor conversion to gasoline and lighter components, high coke production and generation of excessive temperature during the catalyst regeneration. The excessive regeneration temperatures are considered harmful both to conventional equipment and to the catalyst employed in the cracking process.
The instant process relates to the conversion of both the high and low boiling crude oil fractions contained in residual oils. The process provides the high selectivity to gasoline and lighter components with low coke production as set forth in U.S. Pat. Nos. 4,332,674 and 4,331,533, incorporated herein by reference thereto (generally referred to herein as the "HT Process") while providing improvements over the processes disclosed in such patents.
The instant process relates to the problems of high regenerator and catalyst temperatures. The instant invention enables the use of high catalyst regeneration temperatures by taking advantage of special cracking catalysts capable of providing cracking activity at the high regenerator and catalyst temperatures. The instant process operates at high temperatures and takes advantage of the high conversion and high selectivity to gasoline and products which are gasoline precursors on a once through basis without excessive coke formation.